Method of Making Core-Stiffened Structure

ABSTRACT

A method of making a core-stiffened structure includes the steps of providing a honeycomb core having an adhesive disposed on first and second surfaces thereof, providing a first skin and a second skin, and assembling the first skin, the second skin, and the honeycomb core to form the core-stiffened structure. The method further includes the steps of curing the core-stiffened structure and inhibiting at least one of the first skin and the second skin from protruding into at least one cell of the honeycomb core during the step of curing the core-stiffened structure.

This application is a divisional of U.S. patent application Ser. No.15/050,564, filed 23 Feb. 2016, titled “Method of Making Core-StiffenedStructure,” which is a divisional of U.S. patent application Ser. No.13/521,367, filed 10 Jul. 2012, titled “Method of Making Core-StiffenedStructure,” both of which are incorporated herein for all purposes.

1. FIELD OF THE INVENTION

The present application relates in general to the field ofcore-stiffened structures.

2. DESCRIPTION OF RELATED ART

Composite structures often comprise honeycomb core disposed between andadhesively bonded to an inner skin and an outer skin. One example ofsuch honeycomb core is a honeycomb core 101, shown in FIG. 1. Generally,honeycomb core 101 includes a plurality of cells 103 (only one labeledfor clarity) defined by cell walls 105 (only one labeled for clarity).Each of the plurality of cells 103 exhibits a width W. Typically, theplurality of cells 103 have substantially the same width W but, in someimplementations, some cells 103 of the plurality of cells 103 may havedifferent widths W than other cells 103 of the plurality of cells 103.

Traditionally, core-stiffened structures have been limited to the use ofhoneycomb core 101 having cell widths W of less than about 6 mm. Atlarger widths W, as shown in FIG. 2, cell walls 105 fail to providesufficient support for inner skin 201 and outer skin 203 during “curing”of the core-stiffened part, which entails heating the assembledcore-stiffened part under pressure. As a result, portions of inner skin201 and portions of outer skin 203 undesirably extend into cells 103 ofhoneycomb core 101. Thus, while core-stiffened structures made fromlarger-celled honeycomb core 101 weigh less than similar structures madefrom small-celled honeycomb core 101, the manufacture of large-celledcomposite structures has been limited.

Traditionally, core-stiffened composite structure has been sealed fromintrusion of moisture. Some typical core materials are subject tomoisture absorption or corrosion resulting from trapped moisture withinthe core. The sealing of the core edges is done by ramping one skinalong a bevel in the core until both skins contact each other andcomplete a seal around the periphery of the core. During the cure cycle,the pressure on the ramp surface of the core may push the core in adirection lateral to the tool. In order to prevent such a distortion ofthe core, typically material is added to the skin in the proximity ofthe ramp in order to stabilize the skins from lateral distortion of thecore during the cure cycle. As such, the skin is thicker than thestructural application requires so as to prevent lateral distortion ofthe core during the cure cycle.

A similar situation exists for core stiffened composite structure whereone skin is not parallel to the other skin. Such a scenario includes therisk of the core material being pushed laterally along the tool surface.In order to prevent such a distortion of the core material, additionalmaterial is added to the core material and/or to the skins in order toresist the lateral force, and therefore resist core distortion.

There are many methods for processing honeycomb core compositestructures well known in the art; however, considerable room forimprovement remains.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the application are setforth in the appended claims. However, the application itself, as wellas a preferred mode of use, and further objectives and advantagesthereof, will best be understood by reference to the following detaileddescription when read in conjunction with the accompanying drawings, inwhich the leftmost significant digit(s) in the reference numeralsdenote(s) the first figure in which the respective reference numeralsappear, wherein:

FIG. 1 is a stylized, plan view of a portion of a conventional honeycombcore;

FIG. 2 is a stylized, cross-sectional view of a portion of aconventional, core-stiffened structure utilizing large-celled honeycombcore;

FIG. 3 is a stylized, side, elevational view of a core-stiffenedstructure according to the present application;

FIG. 4 is a stylized, cross-sectional view of a portion of honeycombcore used in the core-stiffened structure of FIG. 3, taken along theline 4-4 in FIG. 3;

FIG. 5, is a stylized, exploded, cross-sectional view of a firstembodiment of the core-stiffened structure of FIG. 3;

FIG. 6 is a stylized, plan view of a portion of the honeycomb core ofFIG. 4 with adhesive applied to a surface thereof;

FIG. 7 is a stylized, cross-sectional view of the core-stiffenedstructure of FIG. 5 in a configuration ready for curing or processing;

FIGS. 8-10 are stylized, cross-sectional views of the core-stiffenedstructure of FIG. 3 depicting a second illustrative embodiment of amethod for making a core-stiffened structure according to the presentapplication;

FIGS. 11-14 are stylized, cross-sectional views of the core-stiffenedstructure of FIG. 3 depicting a third illustrative embodiment of amethod for making a core-stiffened structure according to the presentapplication;

FIG. 15 is a stylized, side, elevational view of a core-stiffenedstructure according to and alternative embodiment of the presentapplication;

FIGS. 16 and 17 are stylized, cross-sectional views of thecore-stiffened structure of FIG. 3 depicting a fourth illustrativeembodiment of a method for making a core-stiffened structure accordingto the present application; and

FIG. 18 is a stylized, cross-sectional view of the core-stiffenedstructure of FIG. 3 depicting another illustrative embodiment of amethod for making a core-stiffened structure according to the presentapplication.

While the application is susceptible to various modifications andalternative forms, specific embodiments thereof have been shown by wayof example in the drawings and are herein described in detail. It shouldbe understood, however, that the description herein of specificembodiments is not intended to limit the application to the particularforms disclosed, but on the contrary, the application is to cover allmodifications, equivalents, and alternatives falling within the spiritand scope of the application as defined by the appended claims.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Illustrative embodiments of the present application are described below.In the interest of clarity, not all features of an actual implementationare described in this specification. It will of course be appreciatedthat in the development of any such actual embodiment, numerousimplementation-specific decisions must be made to achieve thedeveloper's specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure.

In the specification, reference may be made to the spatial relationshipsbetween various components and to the spatial orientation of variousaspects of components as the devices are depicted in the attacheddrawings. However, as will be recognized by those skilled in the artafter a complete reading of the present application, the devices,members, apparatuses, etc. described herein may be positioned in anydesired orientation. Thus, the use of terms such as “above,” “below,”“upper,” “lower,” or other like terms to describe a spatial relationshipbetween various components or to describe the spatial orientation ofaspects of such components should be understood to describe a relativerelationship between the components or a spatial orientation of aspectsof such components, respectively, as the device described herein may beoriented in any desired direction.

There is a need for an improved method for processing a honeycombcore-stiffened structure and the core-stiffened structure thereof.Therefore, it is an object of the present application to provide animproved method for processing a honeycomb core-stiffened structure anda core-stiffened structure thereof.

This and other objects are achieved by providing a method of making acore-stiffened structure. The method includes the steps of providing ahoneycomb core having an adhesive disposed on first and second surfacesthereof, providing a first skin and a second skin, and assembling thefirst skin, the second skin, and the honeycomb core to form thecore-stiffened structure. The method further includes the steps ofcuring the core-stiffened structure and inhibiting at least one of thefirst skin and the second skin from protruding into at least one cell ofthe honeycomb core during the step of curing the composite structure.

In another aspect, the present application provides a core-stiffenedstructure, including a honeycomb core having first and second surfaces,a first stabilization skin adhesively bonded to the first surface of thecore, and in some embodiments, a second stabilization skin adhesivelybonded to the second surface of the core. The core-stiffened structurefurther includes a first skin adhesively bonded to the firststabilization skin a second skin adhesively bonded to the first skin andthe second stabilization skin, when the second stabilization skin isused.

In yet another aspect of the present application, a core-stiffenedstructure assembly is provided. The structure assembly includes ahoneycomb core having a first surface and a second surface and defininga plurality of cells and passages extending between the plurality ofcells and a first skin disposed on the first surface of the honeycombcore. The core-stiffened structure assembly further includes a secondskin disposed on the second surface of the honeycomb core and a solubleplug disposed in at least one of the plurality of cells .for inhibitingthe first skin and the second skin from protruding into the at least oneof the plurality of cells during curing of the core-stiffened structureassembly.

In another aspect of the present application, a core-stiffened structureassembly is provided. The core-stiffened structure assembly includes ahoneycomb core having a first surface and a second surface and defininga plurality of cells and passages extending between the plurality ofcells and a first skin disposed on the first surface of the honeycombcore. The core-stiffened structure assembly further includes a secondskin disposed on the second surface of the honeycomb core. Further, aplug that can be dissolved by chemical reaction is disposed in at leastone of the plurality of cells for inhibiting at least one of the firstskin and the second skin from protruding into the at least one of theplurality of cells during curing of the core-stiffened structureassembly.

In another aspect, the present application provides a core-stiffenedstructure assembly. The core-stiffened structure assembly includes ahoneycomb core having a first surface and a second surface and defininga plurality of cells and passages extending between the plurality ofcells and a first skin disposed on the first surface of the honeycombcore. The core-stiffened structure assembly further includes a secondskin disposed on the second surface of the honeycomb core and athermoplastic plug disposed in at least one of the plurality of cellsfor inhibiting the first skin and the second skin from protruding intothe at least one of the plurality of cells during curing of thecore-stiffened structure assembly.

In yet another aspect of the present application, a core-stiffenedstructure assembly is provided. The core-stiffened structure assemblyincludes a honeycomb core having a first surface and a second surfaceand defining a plurality of cells and passages extending between theplurality of cells and a first skin disposed on the first surface of thehoneycomb core. The core-stiffened structure assembly further includes asecond skin disposed on the second surface of the honeycomb core and oneof a magnetorheological fluid and a ferrofluid, disposed in at least oneof the plurality of cells for inhibiting at least one of the first skinand the second skin from protruding into the at least one of theplurality of cells during curing of the composite assembly.

In another aspect of the present application, a core-stiffened structureassembly is provided. The core-stiffened structure assembly includes acore, or optionally an insert having a geometry corresponding to ahoneycomb core, a first skin, and a first release film disposed betweenthe first skin and the insert or core. The core-stiffened structureassembly further includes a second skin and a second release filmdisposed between the second skin and the insert or core and between thesecond skin and the first skin.

In another aspect of the present application, a core-stiffened structureassembly is provided. The core-stiffened structure assembly includeshoneycomb core having a first surface and a second surface and defininga plurality of cells and a first skin disposed on the first surface ofthe honeycomb core and a second skin disposed on the second surface. Thefirst and second skin are not sealed together, instead, either the firstor second skin terminates at the edge of the honeycomb core. Anymoisture can drain or dry out through venting of the edges or throughthe skin, if the skin is breathable. The skin that terminates at theedge of the honeycomb core is tailored to prevent overloading of thecore material near the core termination edge by progressively droppingoff plies in the skin before reaching the edge.

The present application provides significant advantages, including: (1)providing a means for utilizing a large-celled honeycomb core incore-stiffened sandwich structures; (2) providing a means for inhibitingface sheets or skins from protruding into cells of a honeycomb coreduring curing of a core-stiffened sandwich structure; (3) reducing thetendency of lateral movement of honeycomb core during manufacture; and(4) simplifying edge details in some embodiments of the core-stiffenedstructures.

The present application represents a method of making honeycombcore-stiffened composite structures comprising large-celled hoheycombcore. For the purposes of this disclosure, the term “honeycomb core”means a core material comprising a plurality of interconnected cellwalls that define a plurality of cells. While many honeycomb corematerials define hexagonal cells, the scope of the present applicationencompasses core materials that define cells of other shapes, such assquare, rectangular, and the like. It should be appreciated thathoneycomb can be of a variety of materials, including but not limitedto, composite materials and metals. Core can be of any shape and canattach to adjacent skins at angles ranging from perpendicular toparallel. Moreover, the term “large-celled honeycomb core” means, forthe purposes of this disclosure, honeycomb core defining cells having awidth dimension of more than about 6 mm.

FIG. 3 depicts an illustrative embodiment of one particularcore-stiffened structure 301 according to the present application.Core-stiffened structure 301 comprises an inner skin 303, an outer skin305, and a honeycomb core 401 (shown in FIG. 4) disposed between andadhesively bonded to inner skin 303 and outer skin 305. It should benoted that inner skin 303 and outer skin 305 preferably comprise aplurality of reinforcing fibers disposed in a polymeric matrix. As shownin FIG. 4, honeycomb core 401 comprises a plurality of cells 403 (onlyone labeled for clarity) defined by a plurality of interconnected cellwalls 405 (only one labeled for clarity). The present application isparticularly useful when using honeycomb core 401 having cells 403 thatexhibit a width W that is greater than about 6 mm.

FIG. 5 depicts a first illustrative embodiment of a method for makingcore-stiffened structure 301 according to the present application. Inthe illustrated embodiment, an inner stabilization skin 501 is placedagainst an inner side 503 of honeycomb core 401 and a lowerstabilization skin 505 is placed against an outer side 507 of honeycombcore 401. It should be appreciated that in some embodiments only onestabilization skin may be required. For example, if outer skin 305 isthick enough, then lower stabilization skin 505 is not required toprevent outer skin 305 from deforming into cells 403 of honeycomb core401. It should be noted that an adhesive (not shown in FIG. 5) isapplied to inner surface 503 of honeycomb core 401 and to outer surface507 of honeycomb core 401. Preferably, the adhesive is applied in areticulating process, resulting in adhesive 601 substantially coveringcell walls 405 at inner surface 503 and outer surface 507 of honeycombcore 401, as shown in FIG. 6. The adhesive, such as adhesive 601, bondsinner stabilization skin 501 and outer stabilization skin 505 tohoneycomb core 401.

Referring again to FIG. 5, inner stabilization skin 501 and outerstabilization skin 503 are very thin, such as one or two plies offiber-reinforced composite material. Stabilization skins 501 and 503 maybe perforated, porous, or substantially solid without passages extendingtherethrough. It should be noted that inner stabilization skin 501 andouter stabilization skin 505 may be substantially fully “cured,” i.e.,the polymeric matrix is substantially fully cross-linked, if thepolymeric matrix comprises a thermosetting polymer, or the polymericmatrix is in a hardened state, if the polymeric matrix comprises athermoplastic polymer. Alternatively, if the polymeric matrix of innerstabilization skin 501 and outer stabilization skin 505 is athermosetting polymer, inner stabilization skin 501 and outerstabilization skin 505 may be only cured to an extent such that innerstabilization skin 501 and outer stabilization skin 505 do notsubstantially deform into cells 403 of honeycomb core 401 duringprocessing. In such an embodiment, adhesive may not be required betweeninner stabilization skin 501 and inner skin 303, as well as betweenouter stabilization skin and outer skin 305.

Still referring to FIG. 5, outer skin 305 is placed in contact withouter stabilization skin 505 and inner skin 303 is placed in contactwith inner stabilization skin 501. In the illustrated embodiment, innerskin 303 contacts outer skin 305 in areas where inner skin 303 does notcontact inner stabilization skin 501 and outer skin 305 does not contactouter stabilization skin 505. Adhesive may be used between innerstabilization skin 501 and inner skin 303, as well as between outerstabilization skin 505 and outer skin 305.

It should be noted that, in a preferred embodiment, outer skin 305 isfirst placed onto a mold or tool 701 (shown in FIG. 7). It should benoted, however, that one or more other plies or layers, such as abreather ply, may be disposed between outer skin 305 and tool 701. Outerstabilization skin 505 is then located on and placed onto outer skin305. Honeycomb core 401, with adhesive applied to inner surface 503 andouter surface 507 of honeycomb core 401, is then placed onto outerstabilization skin 505, such that outer surface 507 is adjacent outerstabilization skin 505. Inner stabilization skin 501 is then placed ontohoneycomb core 401, such that inner surface 501 of honeycomb core 401 isadjacent inner stabilization skin 501. Inner skin 303 is then placed oninner stabilization skin 501, extending onto outer skin 305.

FIG. 7 depicts assembled core-stiffened structure 301 on tool 701.Bagging material 703 extends over core-stiffened structure 301 and ontotool 701. A vacuum is generated between bagging material 703 and tool701 during processing or curing to consolidate components ofcore-stiffened structure 301 and to extract gases from core-stiffenedstructure 301 during processing. Core-stiffened structure 301 is thenprocessed or cured using heat and, preferably, pressure, to form aconsolidated core-stiffened structure 301.

While stabilization skins 501 and 505 are depicted as extending only tothe edges of honeycomb core 401, the scope of the present application isnot so limited. Rather, as inner stabilization skin 501 and/or outerstabilization skin 505 may, in certain embodiments, extend beyond theedges of honeycomb core 401.

FIGS. 8-10 depict a second illustrative embodiment of a method formaking core-stiffened structure 301 according to the presentapplication. In the illustrated embodiment, cell walls 405 of honeycombcore 401 define openings 801 extending between cells 403. Rather thanusing stabilization skins 501 and 505, a support plug 803 is placed ineach of the plurality of cells 403. Adhesive 601 is depicted inreticulated form so as to provide a fillet of adhesive between innersurface 503 and inner skin 303, and between outer surface 507 and outerskin 305. Plugs 803 extend from inner surface 503 to outer surface 507of honeycomb core 401. Plugs 803 support inner skin 303 and outer skin305 in areas between cell walls 405, thus inhibiting inner skin 303 andouter skin 305 from protruding into cells 403 during processing orcuring. It is preferred that plugs 803 are configured so as to beremovable after processing or curing; however, plugs 803 may also bepermanent and reside within core 401 during the life of core-stiffenedstructure 301.

Openings 801 are to introduce fluid flow within core 401. The fluid flowcould be gas or liquid. Flow through core 401 can be utilized tointroduce heat for manufacturing purposes, to utilize the volumecontained in the core to store a liquid such as fuel, or to introduce awashout fluid to dissolve or chemically react to the solid material ofplugs 803. Furthermore, flow through core may be used to transfer heatin order to provide ice prevention. In addition, flow through core maybe used to transfer heat in order to change heat signature duringservice of structure 301. Flow through the core may also be used forpressure relief for a gradient, or to build up pressure in the volumewithin core 401. In an alternative embodiment, openings through at leastone of the inner skin 303 or outer skin 305 provide fluid flow, in lieuof or in addition to, openings 801 through core 401.

In one embodiment, plugs 803 comprise a soluble material. In a preferredembodiment, a solvent, such as water, is flushed through honeycomb core401, as indicated by arrows 901, via openings 801 to erode and removeplugs 803 after core-stiffened structure 301 has been processed orcured, as shown in FIGS. 9 and 10. In such an embodiment, plugs 803 maycomprise, for example, a eutectic salt, sodium silicate-bonded sand,polyvinyl alcohol-bonded ceramic microspheres, or the like.Alternatively, plugs 803 may comprise a thermoplastic material that ismelted and evacuated from honeycomb core 401 via openings 801. In otherembodiments, plugs 803 may comprise a magnetorheological fluid, aferrofluid, Or the like, which become solid or semi-solid in thepresence of a magnetic field and which become liquid when the magneticfield is removed. Alternatively, plugs 803 may comprise a clay, such asbentonite, which is removed from honeycomb core 401 via openings 801 byvibrating core-stiffened structure 301. Moreover, plugs 803 may take onthe form of a plurality of beads disposed in each of the plurality ofcells 403, such that the beads are small enough to pass through openings801 after core-stiffened structure 301 is processed or cured. Moreover,plugs 803 may be configured to be physically compromised through achemical reaction, and thus evacuated from core 401 in a solid, liquid,or gaseous state. It is preferred that plugs 803 are configured so as tobe removable after processing or curing; however, plugs 803 may also bepermanent and reside within core 401 during the life of core-stiffenedstructure 301.

While plugs 803 are illustrated in FIGS. 8 and 9 as substantiallyfilling cells 403 of honeycomb core 401, the scope of the presentapplication is not so limited. Rather, plugs 803 may not fully extendbetween cell walls 405, as long as sufficient support is provided toinner skin 303 and outer skin 305 to inhibit inner skin 303 and outerskin 305 from protruding into cells 403 of honeycomb core 401 duringprocessing or curing. For example, plugs 803 may exhibit a plurality oflegs extending from a central focal point or line. Preferably, plugs 803not only exhibit strength to prevent skins from compressing, but alsoexhibit strength in the lateral direction to prevent lateral deformationof core 401 during processing. Plugs 803 may also exhibit opposing capssupported by an thin axial member such that the caps provide maximumsupport of inner skin 303 and outer skin 305 while the thin axialmember. Preferably, a gap between the caps and the cell walls of core401 allow space for fillets of adhesive between skins 303 and 305 andcore 401.

FIGS. 11-14 depict a third illustrative embodiment of a method formaking core-stiffened structure 301. In the illustrated embodiment,processing or curing of core-stiffened structure 301 is accomplished intwo steps. In the first step, an insert 1101 corresponding to thegeometry of honeycomb core 401 (best shown in FIG. 13) is placed betweeninner skin 303 and outer skin 305. An inner release film 1103 isdisposed between insert 1101 and inner skin 303 and an outer releasefilm 1105 is disposed between insert 1101 and outer skin 305. Releasefilm 1103 and 1105 comprise, in one embodiment, “peel-ply” material. Asshown in FIG. 12, bagging material 1201 is placed over inner skin 303,extending onto tool 701. Inner skin 303 and outer skin 305 are then atleast partially cured or processed to achieve at least a semi-rigidstate.

Referring now to FIG. 13, inner skin 303 is separated from outer skin305 and insert 1101 is replaced with honeycomb core 401, having adhesiveon inner surface 503 and outer surface 505, as discussed herein. Anadhesive layer 1301 is disposed between inner skin 303 and outer skin305 in areas where inner skin 303 and outer skin 305 abut. FIG. 14depicts core-stiffened structure 301 assembled and ready for curing orprocessing, with a bagging material 1401 extending over inner skin 303and onto tool 701. Core-stiffened structure 301 is then processed,preferably with heat and, in some situations pressure, to adhesivelybond inner skin 303 to outer skin 305 and honeycomb core 401 and toadhesively bond outer skin 305 to honeycomb core 401.

FIG. 15 depicts another illustrative embodiment of one particularcore-stiffened structure 301 according to the present application.Core-stiffened structure 301 comprises an inner skin 303, an outer skin305, and a honeycomb core 401 (shown in FIG. 4) disposed between andadhesively bonded to inner skin 303 and outer skin 305. It should benoted that inner skin 303 and outer skin 305 preferably comprise aplurality of reinforcing fibers disposed in a polymeric matrix. As shownin FIG. 4, honeycomb core 401 comprises a plurality of cells 403 (onlyone labeled for clarity) defined by a plurality of interconnected cellwalls 405 (only one labeled for clarity). Inner skin 303 and outer skin305 are not sealed together; instead, inner skin 303 terminates at aperipheral edge 1503 of the honeycomb core 401. Any moisture can drainor dry out through peripheral edge 1503 of the honeycomb core 401. Ifeither inner skin 303 or outer skin 305 is breathable, then moisturewithin honeycomb core 401 can also drain or dry out through breathableskin 303 or 305. Preferably, inner skin 303 does not abruptly terminateat peripheral edge 1503 of the honeycomb core 401; instead inner skin303 steps down via steps 1501 by progressively dropping off at least oneply in inner skin 303 before reaching peripheral edge 1503. Theprogressive dropping off in plies of inner skin 303 is tailored toprevent overloading of the honeycomb core 401 near the core peripheraledge 1503. It should be appreciated that the dropping of plies isexemplified in steps 1501 shown in FIG. 15; however, steps 1501 may takeon a wide variety of configurations depending upon the thickness ofinner skin 1501 as well as the predicted loading of core-stiffenedstructure 301.

Core-stiffened structure 301 illustrated in FIG. 15 can be manufacturedby the methods of manufacture disclosed herein. However, because core401 is left exposed about peripheral edge 1503, the method ofmanufacture illustrated in FIGS. 8-10 is particularly well suited formanufacturing the embodiment of core-stiffened structure 301 shown inFIG. 15. The embodiment shown in FIG. 15 is configured to survive inhigh strain environment while being extremely light due to the lack oframps between inner skin 303 and outer skin 305.

FIGS. 16 and 17 depict another illustrative embodiment method for makingcore-stiffened structure 301 according to the present application. Inthe illustrated embodiment, processing or curing of core-stiffenedstructure 301 is preferably accomplished using out-of-autoclavematerials that do not require an autoclave to provide high temperatureand pressure. The illustrated embodiment involves two primary steps. Inthe first step, inner skin 303 is laid against a caul 1601 and sealedthereto with bagging material 1201A. Similarly, outer skin 305 is laidagainst tool 701 and sealed thereto with bagging material 1201B.Honeycomb core 401 which is to be used in core-stiffened structure 301is sandwiched between bagging materials 1201A and 1201B. Next, asubsequent bagging material 1201C is placed in sealing contact with tool701 so as to enclose caul 1601, inner skin 303, core 401, and outer skin305. In an alternative embodiment, tool 701 is completely enclosed bybagging material 1201. In another alternative embodiment, baggingmaterial 1201C is omitted while pressure from caul 1601 is used toprovide pressure between inner skin 303, core 401, and outer skin 305.Inner skin 303 and outer skin 305 are allowed to cure while a separatevacuum is pulled on inner skin 303, outer skin 305, and on the assemblyvia bagging materials 1201A, 1201B, and 1201C. The vacuum on inner skin303 and outer skin 305 prevents inner skin 303 and outer skin 305 fromsagging and deforming into the cells of core 401. During the curingprocess, any physical deformations in core 401 are transposed into innerskin 303 and outer skin 305 which provides for improved structuralcharacteristics within core-stiffened structure 301. At this point inthe process, core is not bonded to inner skin 301 and outer skin 305 dueto lack of adhesive and the barrier provided by bagging material 1201Aand 1201B.

The second step involves bonding core 401 to inner skin 303 and outerskin 305. Bagging materials 1201A and 1201B are removed. In addition,adhesive 601 is applied to core 401, preferably through a reticulatingprocess. Adhesive may also be applied directly between inner skin 303and outer skin 305. During this second step of the process, baggingmaterial 1201 is preferably used to apply pressure to the final curingstep for core-stiffened structure 301. However, caul 1601 may be used inlieu of, or in addition to, bagging material 1201. It should beappreciated that the embodiment of core-stiffened structure 301 shown inFIG. 15 may also be manufactured using the method disclosed hereinregarding FIGS. 16 and 17.

FIG. 18 depicts another illustrative embodiment method for makingcore-stiffened structure 301 according to the present application. Inthe illustrated embodiment, processing or curing of core-stiffenedstructure 301 is preferably accomplished using out-of-autoclavematerials that do not require an autoclave to provide high temperatureand pressure. Outer skin 305 is placed against tool 701. Core 401 isplaced against outer skin. Adhesive is used to bond inner skin 303 andouter skin 305 to core 401. Cells 403 within core 401 are substantiallyfilled with a plurality of flexible spherical balls, the spherical ballsbeing filled with a gas. Inner skin 303 is placed against core 401.Bagging material 1201 is used to create a vacuum seal between theassembly and tool 701. Core 401, spherical balls, inner skin 303 andouter skin 305 are subjected to vacuum and heat, thereby causing thespherical balls to expand, thereby preventing inner skin 303 and outerskin 305 from sagging into cells 403 of core 401. After curing,temperature and pressure are decreased, thereby causing the volume ofthe spherical balls to decrease. It is then preferred that the sphericalballs are shaken out of core 401 through openings in cell walls of core401. Spherical balls may also be removed by other means, such as beingdissolved by water. In an alternative embodiment, a foam is applied intocells 403 in lieu of the spherical balls. The foam expands, similar tothe spherical balls, when exposed to at least one of vacuum and heat inorder to prevent inner skin 303 and outer skin 305 from sagging ordeforming in core 401 during curing.

While the methods disclosed herein are useful in making compositestructures comprising conventional honeycomb core materials, they areparticularly useful in making composite structures that includehoneycomb core comprising reinforcing fibers disposed in a polymericmatrix.

The particular embodiments disclosed above are illustrative only, as theapplication may be modified and practiced in different but equivalentmanners apparent to those skilled in the art having the benefit of theteachings herein. Furthermore, no limitations are intended to thedetails of construction or design herein shown, other than as describedin the claims below. It is therefore evident that the particularembodiments disclosed above may be altered or modified and all suchvariations are considered within the scope and spirit of theapplication. Accordingly, the protection sought herein is as set forthin the claims below. It is apparent that an application with significantadvantages has been described and illustrated. Although the presentapplication is shown in a limited number of forms, it is not limited tojust these forms, but is amenable to various changes and modificationswithout departing from the spirit thereof.

1. A method of making a core-stiffened structure, comprising: providinga honeycomb core having an adhesive disposed on first and secondsurfaces thereof; providing a first skin and a second skin; assemblingthe first skin, the second skin, and the honeycomb core to form thecore-stiffened structure; curing the core-stiffened structure; andinhibiting the first skin and the second skin from protruding into atleast one cell of the honeycomb core during the step of curing thecore-stiffened structure, comprising: providing a first stabilizationskin in a perforated or porous configuration; placing the firststabilization skin between the first skin and the first surface of thehoneycomb core prior to performing the step of curing the core-stiffenedstructure; providing a second stabilization skin in a perforated orporous configuration; and placing the second stabilization skin betweenthe second skin and the second surface of the honeycomb core prior toperforming the step of curing the core-stiffened structure; wherein thesecond stabilization skin inhibits the second skin from protruding intothe at least one cell of the honeycomb core; and wherein the firststabilization skin inhibits the first skin from protruding into the atleast one cell of the honeycomb core; wherein the first stabilizationskin is substantially fully cured as the core-stiffened structure isassembled; and wherein the adhesive is reticulated and configured toallow migration of fluid through the first skin, the second skin, andthe honeycomb core.
 2. The method according to claim 1, wherein theinhibiting at least one of the first skin and the second skin fromprotruding into the cells of the honeycomb core comprises: providing afirst stabilization skin; and placing the first stabilization skinbetween the first skin and the first surface of the honeycomb core priorto performing the step of curing the core-stiffened structure; whereinthe first stabilization skin inhibits the first skin from protrudinginto the at least one cell of the honeycomb core.
 3. The methodaccording to claim 2, wherein the inhibiting at least one of the firstskin and the second skin from protruding into the cells of the honeycombcore further comprises: providing a second stabilization skin; andplacing the second stabilization skin between the second skin and thesecond surface of the honeycomb core prior to performing the step ofcuring the core-stiffened structure; wherein the second stabilizationskin inhibits the second skin from protruding into the at least one cellof the honeycomb core.
 4. The method according to claim 2, wherein theproviding the first stabilization skin comprises: providing the firststabilization skin in a perforated or porous configuration.
 5. Themethod according to claim 2, wherein the providing the firststabilization skin comprises: providing the first stabilization skin ina substantially solid form.
 6. The method according to claim 2, whereinthe providing the first stabilization skin comprises: providing thefirst stabilization skin in a partially cured state.
 7. The methodaccording to claim 1, wherein the inhibiting at least one of the firstskin and the second skin from protruding into the at least one cell ofthe honeycomb core comprises: at least partially curing the at least oneof the first skin and the second skin prior to performing the step ofassembling the first skin, the second skin, and the honeycomb core toform the core-stiffened structure.
 8. The method according to claim 7,wherein the at least partially curing the at least one of the first skinand the second skin comprises: providing an insert having a geometrycorresponding to the honeycomb core; providing a first release film;disposing the first release film between the first skin and the insert;processing the first skin and the second skin; and removing the insertand the first release film.
 9. A method of making a core-stiffenedstructure, comprising: applying a first skin to a caul and sealingthereto with a first bagging material; applying a second skin to a tooland sealing thereto with a second bagging material; providing ahoneycomb core between the first bagging material and the second baggingmaterial; providing compressive force to the honeycomb core between thecaul and the tool while at least partially curing the first and secondskin so that physical characteristics in the core are transposed intothe first and second skins; and applying adhesive to the honeycomb coreand performing a second curing cycle to directly bond the first skin,second skin, and the honeycomb core together, as well is complete curingof the first and second skins.
 10. The method, according to claim 9,wherein the providing compressive force to the honeycomb core comprises:providing a vacuum enabled by a third bagging material encompassing thefirst skin, the caul, the honeycomb core, and the second skin.Specification
 11. A core-stiffened assembly, comprising: a honeycombcore having a first surface and a second surface and defining aplurality of cells; a first skin disposed on the first surface of thehoneycomb core, the first skin terminating at a peripheral edge of thehoneycomb core; and a second skin disposed on the second surface of thehoneycomb core and extending outside of the peripheral edge of thehoneycomb core; wherein the first skin and the second are separated sothat the honeycomb core is exposed.
 12. The core-stiffened assembly,according to claim 11, wherein: the first skin includes at least onestep so that a thickness of the first skin decreases in the at least onestep before terminating at the peripheral edge of the honeycomb core.13. The core-stiffened assembly according to claim 11, furthercomprising: a thermoplastic plug disposed in at least one of theplurality of cells for inhibiting the first skin and the second skinfrom protruding into the at least one of the plurality of cells duringcuring of the core-stiffened assembly.
 14. The core-stiffened assemblyaccording to claim 11, further comprising: one of a magnetorheologicalfluid and a ferrofluid disposed in at least one of the plurality ofcells for inhibiting the first skin and the second skin from protrudinginto the at least one of the plurality of cells during curing of thecore-stiffened assembly.
 15. The core-stiffened assembly according toclaim 11, further comprising: a first release film disposed between thefirst skin and the honeycomb core; and a second release film disposedbetween the second skin and the honeycomb core and between the secondskin and the first skin.
 16. The core-stiffened assembly according toclaim 11, further comprising: the first skin terminating at a peripheraledge of the honeycomb core; and the second skin extending outside of theperipheral edge of the honeycomb core; wherein the first skin and thesecond skin are separated so that the honeycomb core is exposed.
 17. Thecore-stiffened assembly according to claim 11, further comprising: thefirst skin includes at least one step so that a thickness of the firstskin decreases in the at least one step before terminating at theperipheral edge of the honeycomb core.